Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors and other semiconductor devices. Typically, such devices are fabricated on a substrate as part of an integrated circuit. In the integrated circuit, vertical contacts are often used to interconnect different layers and devices formed at different levels. It is desirable that the contacts have high thermal stability so that high contact reliability can be achieved and high temperature processes can be used after the contacts are formed.
One type of contact provides an interconnect between a silicon region and other region or device of the integrated circuit. This type of contact generally includes an adhesive layer that will adhere well to a contact hole in which the contact is formed and a silicide region that will reduce resistance of the contact at the silicon region. A typical contact includes titanium nitride (TiN) for the adhesive layer and titanium silicide (TiSi.sub.2) for the silicide region. The contact is formed by sputtering titanium into a contact hole and annealing the deposited titanium to form the titanium silicide. Titanium is then reactively sputtered in nitrogen/argon (N.sub.2 /Ar) to form the adhesive layer. Tungsten (W) or other conductor is deposited on the adhesive layer to complete the contact. This contact, however, is not stable at temperatures above 800.degree. C.
To improve thermal stability of the contact, a TiN.sub.x layer has been sputter deposited to form the adhesive layer. The use of TiN.sub.x, however, has been limited due to poor step coverage in high aspect ratio contact holes. Even with collimated sputtering, it is difficult to deposit TiN.sub.x into small and deep contact holes.